This work is a competing continuation of NIH R01 AR44812, "Assessment of Early Articular Changes with Optical Coherence Tomography". As clinical therapeutics have become available for the treatment of osteoarthritis (OA) in animal models and humans, a need has developed for methods that can accurately assess and monitor their effectiveness, particularly at early stages. Current clinical technologies lack the resolution or are cost prohibitive or both for following patients serially, particularly identifying early OA. Therefore, a need exists for a technology to assess changes in OA at relatively high resolutions. Recently we have developed a new technology, optical coherence tomography (OCT), for the high resolution (up to 25X higher than anything in clinical medicine) assessment of cartilage and joint structures. OCT is analogous to ultrasound measuring the backreflection intensity of infrared light rather than sound. Preliminary data suggests it could be a powerful technology for monitoring relatively minor changes in OA, thereby guiding therapeutics. Our hypothesis is that polarization sensitive OCT (PS-OCT), along with structural OCT imaging, could be a powerful technology for assessing OA changes at high resolution and allow the accurate monitoring of therapeutics. These objectives will be obtained through the following specific aims: 1. The primary focus of this aim will be to understand how different collagen types, concentrations, and orientations in human joint structures affect PS-OCT imaging. 2. The primary focus of this aim will be to understand how different collagen types, organization, concentrations, and orientations in an animal model of OA affect PS-OCT imaging. 3. The primary focus of this aim will be the continued development of an OCT endocatheter. 4. In patients undergoing arthroscopy for routine partial menisectomies, OCT imaging will be performed of the articular cartilage to determine OCTs efficacy for assessing high resolution changes leading to OA. 5. In patients undergoing microfracture during arthroscopy for the treatment of localized OA, OCT imaging will be performed of adjacent articular cartilage.